Electron discharge device



Patented Mar. 15, 1%32 SYLVTESTER CROWLEY, OF'HILLSIDE, JERSEY, ASSIGNOB T0 DE FOREST RADIO COMPANY, OF PASSAIC, NEW JERSEY, A CORPORATION OF DELAWARE ELECTRON DISCHARGE DEVICE I10 Drawing. Original application filed March 1, 1924, Serial No. 696,396. Divided and. this application filed March 14, 1930. Serial No. 435,970.

This invention relates to electron discharge devices and more particularly to the means by Whig; the same are exhausted.

The objects of the invention are to enable an electron discharge device to be manufactured in less time than heretofore; to re duce the time and expense involved in obtaining a high degree of evacuation of the device; to employ a chemical clean-up agency for obtaining part of the evacuation; to employ'a flash as well as a chemical clean-up agency; to employ a chemical clean-up agency and flash adapted to be applied simultaneouslyand put into effect at different times; to enable the chemical clean-up agency and flash to be put into effect by use of hi h frequency or by plate bombardment; to o tain an improved method of manufacture; to secure sim licityof construction and operation, and to o tain other advantages and results as may be brought out in the following description.

In the manufacture ofelectron discharge devices, it has become more or less common practice to employ a filament which includes the element thorium as the emissive substance. Thorium oxidizes quite readily and consequently the filament as inserted in an electron discharge device contains exposed portions of thorium oxide rather than pure thorium. In order to reduce thorium oxide to thorium, it has become common practice to employ a flash of some suitable material, of which magnesium is the one most generally used. The operation is ordinarily carried out by applying a small or ion of magnesium to the plate and then after the tube is evacuated as much as possible by the pump, the plate is heated to a point where the magnesiumwill flash and the resulting vapor will operate to reduce the thorium oxide to thorium. The present invention contemplates means for first obtaining a partial vacuum by means of a pumpso as to materially reduce the time during which the electron discharge device has to be connected with the pump for the purpose of evacuation, and then high evacuation is obtained by other means, after which the magnesium or other material may be flashed similar to the manner in which that operation has been carried on heretofore. In order to obtain the high vacuum by means other than pumping, I employ a chemical which is flashed similar to the magnesium, preferably before the magnesiumis flashed, said chemical obtaining a high state of evacuation of the tube by means or reduction of the residual gases within the tube. The magnesium could not be used practically for this purpose, both because it is not sufliciently active to reduce the residual gases to the necessary amount, nor is it practical to flash the magnesium until a very much higher degree of evacuationhas been effected .than is required in connection with the present invention.

I preferably employ in combination wit a flash of magnesium or other suitable mate rial, chemical cleanup agency of phosphorus. The advantage of employing phosphorus is that it may be flashed at a lower temperature than magnesium and also that phosphorus will eifectively reduce the residual gases when flashed while the device is not in such a high state of evacuation as necessary to obtain reduction by means of magnesium. I may also state that very good results are obtained by use of red or amorphous phosphorus. Since phosphorus in this state is more convenient to handle and does not have to be protected until ready to be flashed, it is the better variety to use.

.In order to apply the phosphorus to the plate or other part from which it is to be flashed, I preferably mix the phosphorus and magnesium in the nature of a paste or paint and apply it With a brush or in any other suitable manner. As much of the plate as desired-may be covered with the mixture, al-.

though it will probably be sufficient in most casesto employ only a good size spot on the plate. I do not wish it to be understood that it is necessary to mix the phosphorus and magnesium, and indeed, in some instances it may be highly desirable not to mix the two.

The flashing of the phosphorus and magnesium, as indicated above, takes place at different times, phosphorus being flashed first in order to reduce the residual. gases and obtain a higher degree of evacuation, after which the magnesium is flashed in order to reduce the thorium oxide of the filament to thorium. There are a number of ways of obtaining the flash of the phosphorus and magnesium one instance of which is the usual method of plate bombardment. The tem erature of the plate is raised by means an initial electron emission to such a point as to cause the phosphorus to vaporize and combigne with the residual gases. Continued bomhardment of, the plate will raise the temperature to a higher degree and thus obtain a subsequent flashing of the magnesium. The flashing of magnesium has heretofore been effected by means of high frequency current, and this may also be utilized for flashing the. phosphorus. In order to obtain a marked time difference between the flashing of the phosphorus and ma nesium, the phosphorus may be applied to the plate toward one end of the electron discharge device and the magnesium applied to the plate toward the other end, so that the high frequency coil may be manipulated to operate only on the end of the plate to which the phosphorus is applied, so

as to flash the phosphoruseand then moved along so as to operate upon the other end of the plate and flash the magnesium.

It is apparent that both the phosphorus and the magnesium provide clean-up agents both of 'which are flashed but at difl'erent temperatures. In the broad aspect of this invention any two suitable a ents could be used 7 which are adapted to be temperatures. The term flash as used in Obviously other detail changes and modifications may be made in the manufacture 1 and use of my improved electron discharge device, and I do not wish to be understood as limiting myself tothe exact structure or ashed at different device.

5. An electron discharge device having a plate electrode, a chemical clean-up agent applied to one part of said plate, and a flash material .applied to a different part of said late. p In testimony whereof I have hereunto set my hand on this 7th day of March A. D.,

SYLVESTER W. CROWLEY.

method described, except as set forth in the following claims when construed in the light of theprior art.

This case is a division of application Serial No. 696,396 filed March 1, 1924.

What is claimed is 1. The method of manufacturing an electron discharge device having a thoriated filament which comprises applyin a chemical clean-up agent and a filament ash material at different parts of said device, energizing the clean-u agency and subsequently energizing the ash material.

2. The method according to claim 1 in which the energization of the clean-up agent .nd the flash material is effected by high frequency currents.

3. The method of manufacturing electron discharge devices which comprises applying a chemical clean-up agent to one part of said device, applying a flash material at a difl'erent part of said device, subjecting said clean-up agent to the action of ahigh-frequency field, and moving said field to sub- 

